The long-term objective of this proposal is to better understand the interactions between the Pseudomonas aeruginosa and innate immunity. Microbial pathogenesis is complex, involving numerous components from both the pathogen and the host. In preliminary studies, we have isolated several virulence factors of P. aeruginosa that are relevant in mammalian pathogenesis using Drosophila model host system. These results suggest that invertebrates could serve as inexpensive hosts to reveal novel mechanisms used by the pathogen to defeat innate immunity. Similarly, numerous studies have demonstrated that the innate immunity pathways of Drosophila and mammals have been conserved during the divergent evolution. However, contrary to previous studies, for the first time, our preliminary data indicate that Drosophila Toll signaling is important for resistance to infection by P. aeruginosa, a Gram-negative bacterium. Our central hypothesis is that Toll mediated immunity is required during antagonistic interactions with P. aeruginosa. Taking advantage of the genetics and rapid life cycle of Drosophila, we propose one specific aim to: (i) screen for P. aeruginosa virulence genes specifically against Drosophila Toll signaling. Upon completion of this work, we expect to improve our understanding of the dynamic interplays between Toll mediated innate immunity and P. aeruginosa virulence. [unreadable] [unreadable] [unreadable]